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I have three Internet connections at home, they are not connected to each other in any possible way, they are from three different ISPs

enter image description here

  • FTTC #1 , the white modem and the black and white router
  • FTTC #2 , the BT black modem/router
  • EE 4G , the white square modem/router

My two years old son uses two iPads at the same time, one is connected to FTTC #1 and the second is connected to EE 4G. Rest of the house uses FTTC #2. Obviously we all use WiFi.

This morning I was downloading a huge amount of files from an FTP server using my laptop that is connected to FTTC #2 over WiFi. Both iPads could not connect to their networks. at first I thought something is wrong but once I stopped downloading both iPad went back online. To be 100% sure I resumed the download and all the sudden both iPads had problems authenticating to their networks, one of them kept trying to connect while the other kept asking for password repeatedly.

I always assumed air was a huge pipe that you can never block and cause congestion?!

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  • are you sure the ipads are connecting to the right AP? – Keltari Feb 2 '15 at 21:30
  • 100% sure. iPad one was connected FTTC #1 and iPad two was connected to EE 4G. The only possibility that I could think of is that I have caused a congestion and they all use the same channel – Ulkoma Feb 2 '15 at 21:32
  • Regarding that device covered in plastic tape(?): could you perhaps give it some ventilation before it cooks? Other than that, have you set the wireless routers to different channels (1, 6, or 11: How to boost your WiFi speed by choosing the right channel) so that they don't interfere with each other? – Andrew Morton Feb 2 '15 at 21:38
  • I'll remove the plastic tape, I have not changed the default settings for the channels as I know less than nothing about this aspect, maybe they are all on the same channel. The question is: can I flood a channel? does this mean I can attack my neighbors and cause a DoS? – Ulkoma Feb 2 '15 at 21:41
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DoS-ing Wi-Fi with another wireless device is pretty easy, see Why does my microwave kill the Wi-Fi?.

All wireless technologies have to transmit data somehow. Information doesn't just magically appear on another device - a transmission medium and a time frame are always required. For any medium and any time frame there's an amount of data that will saturate it.

Wi-Fi works on 2.4 GHz radio band. It means that it transmits using electromagnetic radiation waves with frequencies around 2.4 GHz, or strictly speaking 2.401-2.495 GHz. This frequency range is divided into 14 partially overlapping channels:

Wi-Fi channels diagram

Most routers will look for neighboring Wi-Fi networks and check which channels they are using, then switch to the least populated channel. Usually only channels 1, 6 and 11 are used because they don't overlap and thus offer best results (channel 14 is unavailable in most countries).

I guess that for some reason your routers don't switch channels properly, possibly because they are very close to each other. (You should keep Wi-Fi devices at least 30 cm away from each other, 1 m is recommended. This applies both for access points and connected devices.) When one device saturates the channel, other connections will drop.

If you want to avoid this issue, try manually setting access points to different channels.

  • In fact I keep all the devices next to each other and sometimes on top of each other. When it happened I had all of them very very close to each other – Ulkoma Feb 2 '15 at 22:06
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As stated the first thing I would look into is to verify that you're connected to different APs.

And that each AP is on a different frequency (also known as channel) so that they do not conflict with each other.

With the only thing in the environment that changes is that you're using heavy bandwidth on one system, I would assume its an issue with one of the above or you would always have issues.

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